Electronic Structure of A$_y$Fe$_{2-x}$Se2 from First Principles

The newly discovered A$_y$Fe$_{2-x}$Se2 iron-selenide material family was studied in a series of first-principles simulations. The electronic structure and magnetic properties of possible vacancy-superstructure phases A$_2$Fe$_3$Se$_4$ and A$_2$Fe$_4$Se$_5$, as well as the possible parental phase of superconductivity AFe2Se2 were examined. It was discovered that AFe2Se2 ground state is a SDW-AFM metal without hole Fermi-surface, thus FS-nesting is absent and its magnetism is very likely to be local moment; A$_2$Fe$_3$Se$_4$ is a Mott insulator with SDW-AFM magnetism; A$_2$Fe$_4$Se$_5$ shows block-spin AFM ground state with 400$\sim$600 meV band gap. Under high pressure, the A$_2$Fe$_4$Se$_5$ phase exhibits rich and exotic physical properties. \\[4pt] [1] Chao Cao and Jianhui Dai, Block Spin Ground State and Three-Dimensionality of (K,Tl)$_y$Fe$_{1.6}$Se$_2$, \textit{Phys. Rev. Lett.} \textbf{107}, 056401 (2011)\\[0pt] [2] Chao Cao and Jianhui Dai, Electronic structure and Mott localization of iron-deficient TlFe$_{1.5}$Se$_2$ with superstructures, \textit{Phys. Rev. B} \textbf{83}, 193104 (2011)\\[0pt] [3] Chao Cao and Jianhui Dai, Electronic Structure of KFe$_2$Se$_2$ from First-Principles Calculations, \textit{Chin. Phys. Lett.} \textbf{28}, 057402 (2011)